Isolation of Gallionella ferruginea by use of formalin

In seven out of ten separate trials, contaminants in cultures of Gallionella ferruginea were eliminated by incubation of the crude culture for 1–2 days in Wolfe's medium containing 0.5% formalin. Purity was judged microscopically and also by the absence of contaminant growth in a variety of heterotrophic and autotrophic test media. Parallel cultures not treated with formalin exhibited growth of contaminants in most test media. Pure cultures of G. ferruginea have been maintained by serial transfer for at least 14 months and in continuous flow culture for at least 3 months. Preservation has been possible by storage at −80 °C in 15% glycerol. G. ferruginea in impure culture grew as a microaerophilic band closer to the surface of the fluid in the culture bottles than it did in pure culture; in the pure culture state it grew in a dense mat on the surface of the submerged ferrous sulfide agar. This difference probably resulted from the absence of oxygen-utilizing contaminants in the pure state.